[PATCH v4 00/10] Untracked cache improvements

Here is a new version of a patch series to improve the untracked cache feature.

This v4 implements core.untrackedCache as a tristate config variable. When it's `true`, Git commands, especially `git status`, should always add the untracked cache and use it, and when `false`, Git commands should remove it. The default though is now `keep` in which case the untracked cache is neither removed nor added, and used if it is there.

Patch 1/10 is a small bugfix that has not changed since v3.

Patch 2/10 to 4/10 add some small features that are missing. The only chqnge there since v3 is that we are now using `report()` to display verbose information, thanks to Duy.

Patchs 5/10 to 7/10 are some refactoring to prepare for the following patchs. Among them 6/10 is the result of merging two patchs from v3, thanks to Eric.

Patch 8/10 deals with the "ident" field in "struct untracked_cache" and is mostly the same as in v3. The difference is just a small bug fix to prevent a crash.

Patch 9/10 adds core.untrackedCache. It has been changed compared to
v3 in the following ways:
  - the config variable is now a tristate, thanks to Junio,
  - we use `switch` to deal with different values, thanks to Torsten,
  - documentation for --test-untracked-cache is improved, thanks to
    David.

Patch 10/10, which contains tests, has been changed to reflect changes in 9/10 and to add a few tests.

So the changes compared to v3 are mostly small updates, and patchs 6/10, 9/10 and 10/10.

The patch series is also available there:

https://github.com/chriscool/git/tree/uc-notifs40

Thanks to the reviewers and helpers.

Christian Couder (10):
  dir: free untracked cache when removing it
  update-index: use enum for untracked cache options
  update-index: add --test-untracked-cache
  update-index: add untracked cache notifications
  update-index: move 'uc' var declaration
  dir: add {new,add}_untracked_cache()
  dir: add remove_untracked_cache()
  dir: simplify untracked cache "ident" field
  config: add core.untrackedCache
  t7063: add tests for core.untrackedCache

 Documentation/config.txt               |  7 +++
 Documentation/git-update-index.txt     | 65 +++++++++++++++++++++++-----
 builtin/update-index.c                 | 62 ++++++++++++++++----------
 cache.h                                |  1 +
 config.c                               | 11 +++++
 contrib/completion/git-completion.bash |  1 +
 dir.c                                  | 70 ++++++++++++++++++++++++------
 dir.h                                  |  2 +
 environment.c                          |  1 +
 t/t7063-status-untracked-cache.sh      | 79 +++++++++++++++++++++++++++++++---
 wt-status.c                            | 13 ++++++
 11 files changed, 260 insertions(+), 52 deletions(-)